An experimental and numerical investigation of adhesive bonding strengths of polymer materials

We employed the Iosipescu shear specimens and butt-joint specimens to measure the shear and tensile strengths of five types of adhesive bonds for brittle poly(methyl methacrylate) and Homalite polymers. In order to examine the possible stress singularities due to property mismatch between the adhesives and polymers, and ensure uniform stress distributions along the bonded interfaces, two optical techniques, photoelasticity and coherent gradient sensing, were employed to record full field, in situ fringe patterns until specimens failed. Direct comparison of finite element analysis and experimental stress analysis of Iosipescu shear specimens showed that along the polymer/adhesive/polymer interface, only a very weak stress singularity existed. Consequently, the stress distributions were quite uniform. Butt-joint tensile experiments verified negligible stress singularities and uniform stress distributions along the interface. However, for some shear specimens with strong bonds, the final failure occurred in a tensile mode at the upper edge, rather than a shear failure mode in the gauge section. Hence, only the lower limits of the shear strength rather than the actual magnitude could be measured.